On your CC? None. If you want to base something like a plerogyra(bubble) or caulastrea(candycane) in the CC then cool. You basically don't want the flesh of the coral rubbing against the CC in any manor.
I have CC and a CC mix in 2 tanks (55&125) and have had sucess with most of my corals. Softies and SPS. I don't put them directly on the substrate though. I like them on the LR instaed. This also places them up closer to the lights. Many debates here on substrates, I like my CC and don't plan on changing any time soon. Good Luck!